David Cameron went for an early morning dip in Lough Erne before breakfast at Wednesday's G8 summit. That set him up nicely for the day's negotiations, where the leaders of the west proceeded to pour cold water over his plans for a big breakthrough on tax evasion.

Make no mistake, the prime minister deserves credit for putting the ownership of shadowy companies and the ease with which multinational companies shift profits round the world on the agenda at the talks. Few would have expected that a year ago.

It was also a modest achievement to get the UK's overseas territories and crown dependencies to sign up to a set of core international principles on exchange of information – something that should have happened a long time ago.

But progress at the summit itself was virtually non-existent. A declaration of G8 principles was a windy document that committed the west's leading industrial nations to do little specific.

The G8 Action Plan was similarly weak. The G8 said information on the beneficial ownership of companies could be achieved through central registries. Plenty of wriggle room, there.

Cameron wanted a couple of other G8 leaders to join him in pressing for public registries, but in the end none did so. All the G8 would agree to was that "some basic company information should be publicly accessible". The bare minimum, no doubt.

Development campaigners said there was a bit more progress on allowing poor countries to be part of a new G8 deal on automatic exchange of tax information, but it remains to be seen when they will be allowed to do so.

There was plenty of pushback on this issue as well, although the prime minister remains hopeful that some developing countries can be part of a pilot scheme to test out the idea. First, though he will have to overcome misgivings about handing over sensitive tax details to countries not deemed competent or trustworthy enough to handle it with care.

So what has changed, if anything? Here, the good news is that the G8 has agreed a broad set of principles. The bad news is that the 10-point plan doesn't actually commit the countries to doing very much. Real progress in tightening up the global regime is going to be painfully slow, and that's a problem because by the time policymakers in the G8 get their act together the tax evaders will have found new ways of hiding their loot from the taxman. As Murray Worthy of War on Want put it: "As always, the devil is in the detail and there are no details."

Who, therefore is to blame for the summit's lack of real progress? Clearly, the G8 countries that put up strong resistance to change need to be named and shamed. This list includes the United States, where the tiny state of Delaware is the tax haven of choice for shell companies.

But Cameron, too, bears responsibility for leaving it until it was too late to start the heavy lobbying that was clearly going to be needed to get the rest of the G8 to move on tax. The If campaign may now regret treating the prime minister with kid gloves in the months running up to the summit.

At his closing press conference, Cameron said there had been "real progress" on tax, with the G8 agreement having the potential to rewrite the global rules on tax and transparency. The key word there was "potential". History suggests there is a long lag between the G8 issuing statements of intent and them actually doing anything.

Lough Erne put tax on the agenda but it is only the start of a long process.